As is known, the degradation of building materials, in particular marble, sandstones, tiles as well as decorative and artistic articles and structures manufactured from such materials is caused by two different kinds of phenomena: chemical phenomena and physical phenomena, both occurring in the presence of water.
A physical phenomenon affecting all the building materials is the one which is due to successive frosting and defrosting of the water absorbed by the pores of the material itself. Such phenomenon results in a variation of the specific volume and in tensions which are capable of causing fractures and/or decohesion (loss of cohesion) or in any case detachment from each other of the individual particles constituting the material.
Another physical phenomenon is the dissolution in water of the limestone contained in marbles as an essential component and in the stones as a binder, with consequent loss of cohesion of the granules.
Of the same importance for the degradation of the materials and manufactured articles and structures exposed to the atmosphere are an aggregation of ehcmical phenomena: these phenomena essentially involve the aggressive attack on the carbonate parts of the material or of the manufactured article or structure by the polluting agents present in the air (e.g., carbon dioxide, sulphur dioxide, nitrogen oxide). Such pollutants react with the material in the presence of water and their concentration is particularly high in the rain at the beginning of the precipitation.
It is known, too, that in order to overcome or at least to sensibly reduce the drawbacks described hereinabove it is necessary to remarkably reduce both the extent of penetration and the velocity of penetration of the water into the material to be protected.
To achieve this purpose, chemical compounds exerting both a water-repellent and a consolidating action are usually applied to the outer surface of the material to be protected.
In order to exert the desired protective action without simultaneously giving rise to accompanying degradtion phenomena or, in any case, undesirable secondary effects, the consolidating/protective agent must possess the following essential properties:
(1) capability of restoring the cohesion between the particles of the surface layer of the degraded material and the underlying integral part; PA0 (2) to give a suitable mechanical resistance to the so-consolidated surface layer; PA0 (3) capability of maintaining, in the consolidated surface layer, characteristics of elasticity in order to prevent --as conversely occurs with other products the --formation of a rigid surface layer with mechanical characteristics different from those of the substrate; PA0 (4) chemical inertia towards the material to be protected/consolidated; PA0 (5) low volatility; PA0 (6) stability to the action of the atmospheric agents to light and to heat; PA0 (7) causing no alterations to the chromaticity of the material; and PA0 (8) capability of retaining in the long run its own solubility properties in order to insure the reversibility of the treatment.
As is known, film-forming substances such as glues, essiccative oils, resins and polymeric substances are often used to consolidate and protect stone materials. References to the use of such substances can be found in the book by Amoroso and Fassina "Stone Decay and Conservation", Elsewier Ed., Amsterdam, 1983.
Among such substances --not all being fully satisfactory for the abovesaid purposes --those most commonly used are: polyethyleneglycols and methylethers thereof, which exhibit, however, a high solubility in water, which limits the use of same to the protection of manufactured articles and structures not exposed to the external atmosphere; polyvinyl acetate and polyvinyl alcohol, which are affected by the drawback of being sensible to water, in which the former, furthermore, hydrolyzes and releases acetic acid; polymethylmethacrylate and acrylic resins in general, which, however, tend to yellowing over time and are not capable of securing a complete protection from SO.sub.2 present in the atmosphere, while the thermosetting acrylic copolymers, endowed with better characteristics, have the drawback of being irreversible; silicone resins which, however, besides the possibility of releasing methanol, exhibit also the drawback of cross-linking, with consequent formation of a product no longer removable; epoxy resins, which tend to yellowing and, due to their structure of thermosetting resins, make it difficult or impossible to carry out reversible treatments; polyester resins, which suffer from the drawback of being sensitive to water (by the effect of which they tend to saponify), and also to cross-link, wherefore they lose the reversibility characteristic.
Such products, which are used in the conservation of stone and tile materials, besides not possessing generally, as illustrated hereinabove, characteristics of stability to chemical and physical aggressive agents, do also drastically reduce the permeability of the treated surface to the air and water vapor. Consequently, the articles and structures exposed to the ourdoors are affected by extremely strong alteration phenomena underneath the impermeable film, due to the action of condensated water inside the same materials.
The use of perfluor-polyethers for the abovesaid purposes, as is described in European patent No. 59,100, has solved the problem of the protection. However such compounds, owing to their being liquids, cannot exert any consolidating action.